The photographic emulsion layers or other layers in a silver halide photographic photosensitive material are often colored so that they absorb light of a specified wavelength.
A colored layer can be formed on the side further from the support than the photosensitive photographic emulsion layer, where it is necessary to control the spectral composition of the light which falls on the photographic emulsion layer. Such a colored layer is known as a filter layer. In cases where there is a plurality of photographic emulsion layers, as in the case of a multi-layer color photosensitive material, filter layers are also established between these emulsion layers.
Light which has been scattered when passing through a photographic emulsion layer or after transmission is reflected at the boundary between the emulsion layer and the support or at the surface of the support on the opposite side from the emulsion layer. In this case, a colored layer can be formed between the photographic emulsion layer and the support or on the opposite side of the support from the photographic emulsion layer to prevent blurring of the image caused by such scattered light. In other words, the occurrence of halation due to this light re-entering the photographic emulsion layer may be prevented. Such a colored layer is know as an anti-halation layer. Anti-halation layers are also located between the emulsion layers in multi-layer color photosensitive materials.
Photographic emulsion layers can also be colored in order to prevent the loss of image sharpness which is due to the scattering of light within the photographic emulsion layer (this phenomenon is generally known as irradiation).
On the other hand, in recent years, recording materials have been proposed which have been sensitized to infrared wavelengths, which is to say recording materials on which the output of a near infrared laser is recorded. For example, the method of forming an image with a so-called scanner system, in which the original is scanned and a silver halide photographic photosensitive material is exposed on the basis of the image signal and a negative image or a positive image corresponding to the original is formed, is known as one method of exposing such a photographic photosensitive material. With this method the use of a semiconductor laser as the recording light source in the scanner system is most desirable. Semiconductor lasers are advantageous in that they are small and cheap, they are readily modulated, they have a longer life than He-Ne lasers and argon lasers for example, and they generate light in the infrared region. If a photosensitive material which is sensitive to the infrared region is used, there is the further advantage that the handling operability is improved since it is possible to make use of a bright safelight.
However, the oscillating wavelength of a semiconductor laser is in the red to infrared range. Thus, a need for sensitive materials which are highly photosensitive to the red to infrared region has arisen.
Sensitizing dyes for spectral sensitization in this region are such that the wavelength dependence of the spectral sensitivity is generally broad. Thus, it is difficult to photosensitize selectively the individual photosensitive layers in a photosensitive material which has a plurality of layers to different laser lights, and color separation is poor.
Moreover, when exposures are made using high density light, such as laser light, of a long wavelength in the red to infrared region, the spreading of the light due to halation and irradiation is pronounced. This causes a marked deterioration in resolution.
Colored layers can be used to prevent the deterioration in color separation and resolution. Since the layers which should be colored are often comprised of hydrophilic colloid, a water soluble dye is generally included in the layer for the purpose of coloration. These dyes must satisfy conditions such as those indicated below:
(1) they must have the proper spectral absorption corresponding to the intended use; PA0 (2) they must be photographically inert. Thus, they must have no deleterious effect in a chemical sense on the performance of the silver halide photographic emulsion layer, which is to say that they should not reduce photographic speed, cause fading of the latent image, or cause fogging; PA0 (3) they should be decolored or dissolved out in the course of photographic processing and leave no deleterious coloration in the photographic photosensitive material after processing; and PA0 (4) they should have excellent storage stability in solution or in photographic materials.
There are many conventional dyes which absorb visible light or ultraviolet light and which satisfy these conditions. They are suitable for improving images in conventional photographic elements which are sensitized to wavelengths of 700 nm and below. The triarylmethane and oxonol dyes in particular are widely used in this connection.
In the past, much effort has been made to discover dyes which satisfy the aforementioned conditions, and many dyes have been suggested.
For example, there are the tricarbocyanine dyes disclosed in JP-A-62-123454, JP-A-63-55544 and JP-A-64-33547, the oxonol dyes disclosed in JP-A-1-227148, the merocyanine dyes disclosed in JP-A-1-234844, the tetraaryl type polymethine dyes disclosed in JP-A-2-216140 and the indoaniline dyes disclosed in JP-A-50-100116, JP-A-62-3250 and JP-A-2-259753. (The term "JP-A" as used herein signifies an "unexamined published Japanese patent application".)
However, there are still very few dyes which can satisfy all the aforementioned conditions. Hence, there are few excellent photosensitive materials which have a high photosensitivity in the infrared region, which have good color separation, and in which halation and irradiation are prevented. Thus, at the present time, it is impossible to realize satisfactorily the characteristics of the semiconductor lasers which have an excellent performance as described above.